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Fine coal dry cleaning using a vibrated gas-1047298uidized bed

Xuliang Yang Yuemin Zhao Zhenfu Luo Shulei Song Chenlong Duan Liang Dong

School of Chemical Engineering amp Technology China University of Mining and Technology 221008 Xuzhou China

a b s t r a c ta r t i c l e i n f o

Article history

Received 25 February 2012

Received in revised form 8 June 2012

Accepted 22 August 2012

Available online 19 September 2012

Keywords

Fine coal

Dry cleaning

Vibrated gas-1047298uidized bed

Segregation

Bubble-driven jigging

Fine coal (minus6 mm) cleaning in a dry way becomes more important with the extensive deployment of the mech-

anized mining and progressively serious water shortage especially in North-West China In this paper we

attempted to use the segregation in a vibrated gas-1047298uidized bed of dissimilar particles to provide a solution to

this problem The effects of several factors including the super1047297

cial air velocity bed height vibration intensityand1047298uidizing timeon the segregation performance wereexperimentally studiedThe bubble-driven jigging mech-

anismwas proposedto explain the separation processThe results showthat the probableerror E values of thesep-

aration of minus6+3 mm and minus3+1 mm size fraction of feed coal samples are 019 and 0175 respectively which

indicates that 1047297ne coal separation using a vibrated gas-1047298uidized bed can provide a simple and ef 1047297cient way for

coal cleaning in dry and cold regions in North-West China

copy 2012 Elsevier BV All rights reserved

1 Introduction

Dry cleaning of 1047297ne coal (minus6 mm) is an important issue in coal sec-

tor especially for China Large amounts of 1047297ne coal are produced during

coal mining as a result of the extensive deployment of the mechanizedmining technology and should be cleaned with the consideration of en-

ergy source conversation and environment protection In addition

Chinas coal reserves are mainly deposited in North-West China where

the arid geological environment and prolonged cold weather per year

present obstacles to the deployment of the coal wet cleaning technolo-

gies Thus it is urgent to develop a novel and ef 1047297cient dry cleaning tech-

nology for 1047297ne coal The cleaning technologies including air dense

medium 1047298uidized bed separator [12] air jigging [3] and FGX separator

[4] provide ef 1047297cient solutions to the dry cleaning of minus50+6 mm coal

Fan et al [56] studied magnetically stabilized 1047298uidized beds for separat-

ing1047297necoal(minus6+1 mm)Luoet al [7] introduced the vibrationenergy

to an air dense medium1047298uidized bed separator in order to provide a so-

lution to1047297necoal (minus6+ 1 mm) cleaningMacpherson et al[89] studied

the density-based separations of 1047297ne coal (minus8+1 mm) in the Re1047298ux

Classi1047297er with an airndashsand dense-medium and vibration Although

these three 1047297ne coal dry cleaning technologies give good separation

results they all encounter obstacles in the way of industrial applications

due to the problems of dense medium recovery product puri1047297cation

and low processing capacity Overall for 1047297ne coal (minus6 mm) there is no

effective dry cleaning technology that can work with great potential for

commercialization

Granular materials in a 1047298uidized bed can segregate due to differ-

ent material properties such as different densities andor sizes [10]

However stable 1047298uidization of coarse particles (+1 mm) that be-

longs to the type D material in the classi1047297cation by Geldart [11] is

very dif 1047297cult by ambient air solely The introduction of vibration en-

ergy to traditional gasndashsolid 1047298uidized beds can1047298uidize the coarsepar-

ticles effectively by enhancing the hydrodynamic interaction betweenair and particles and by eliminating the channeling of air 1047298ow within

the bed The segregation processes that occur simultaneously in vi-

brated gas-1047298uidized beds are solely and entirely by the bubbles [12]

Appropriate bubbling stability is responsible for a stable and effective

segregation behavior due to regular hydrodynamic interaction of the

two-phase 1047298ow [13] In this paper we focus on utilizing a vibrated

gas-1047298uidized bed to clean minus6+1 mm 1047297ne coal and studying the ef-

fects of different operational factors on the separation performance

2 Mechanism

In a vibrated gas-1047298uidized bed of coarse particles with different den-

sities the segregation is mainly caused by the bubbles When a bubble

rises through the granular bed a temporarily disturbed region having

considerable lower solid volume fraction than the surrounding bulk

phase is formed behind the bubble In this region particles with higher

density tend to sink preferentially over the lighter particles which

leads to local particle segregation The hindered settling velocity plays a

key role in this segregating process Brie1047298y high-density particles have

an opportunity to overtake low-density particles by falling rapidly

through the bubbles and also settling faster in the temporarily disturbed

regions Thebubblesimpose a periodic expansion and contraction on the

particle bed thereby causing separation mainly based on density rather

than size This process is analogousto theseparation technique of jigging

[13] and consequently the aforementioned separation mechanism can

be summarized as the bubble-driven jigging mechanism Like traditional

Fuel Processing Technology 106 (2013) 338ndash343

Corresponding author Tel +86 15162110730

E-mail address yangxuliang126com (X Yang)

0378-3820$ ndash see front matter copy 2012 Elsevier BV All rights reserved

httpdxdoiorg101016jfuproc201208019

Contents lists available at SciVerse ScienceDirect

Fuel Processing Technology

j o u r n a l h o m e p a g e w w w e l s e v i e r c o m l o c a t e f u p r o c

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jigging techniques good separation in a vibrated gas-1047298uidized bed also

requires enough bubble-driven jigging cycles In addition the achieve-

ment of optimal segregation is highly sensitive to several operational fac-

tors like the super1047297cial air velocity vibration intensity bed height and

1047298uidizing time for their signi1047297cant effects on the bubble behavior and

the 1047298uidization quality

3 Experimental

31 Coal particle properties

Fine coal is a multi-component granular system and has a consider-

able wide density distribution generally ranging from 12 to 24 gcm3

Thusnarrow size range of the feed is favorable to the particle segregation

basingon densitydifferencewhich will minimize the in1047298uence of particle

size difference on the hindered terminal settling velocity and reduce the

number of dissimilar particles having equal settling velocity For 1047297ne

coal separation using a vibrated gas-1047298uidized bed the ratio of the upper

limit size to the lower one is approximately no more than 31

In this paper two size fractions ieminus6+ 3 mm andminus3+1 mmcoal

were studied and their density distribution is given in Tables 1 and 2

respectively They both belong to high-ash coal which accounts for a con-

siderable large share of 1047297

ne coal in North-West China Both size fractionshave a large amount of high density materials of +18gcm3 of 3847

and 3768 respectively

32 Experimental apparatus

The schematic diagram of the experimental apparatus is shown in

Fig 1 The experimental apparatus of a vibrated gas-1047298uidized bed con-

sists of three main parts gas supply system vibration generating sys-

tem and 1047298uidized bed The 1047297ne coal particles are 1047298uidized in a vertical

cylinder with an inner diameter of 110 mm and a height of 400 mm

which is made from transparent plexiglass Ambient air after 1047297ltering

is dispersed by a sintered metal distributor and then enters the vessel

and 1047298uidizes the granular particles Air pressure is controlled over a

range from 01 to 025 MPa by a valve leading to the atmosphere thatregulates the pressure of the tank The vibrated bed deployed in this

studyis manufactured by China STI Co LTD and itsoperational param-

eters can be easily adjusted by a digital controller to generate vibration

motions with amplitude ranging from 0 mm to 10 mm and frequency

ranging from 1 Hz to 400 Hz OLYMPUS i-SPEED 3 high speed camera

system is used to study the particle motions within the bed in order

to reveal the separation process and verify the bubble-driven jigging

mechanism

33 Segregation evaluation

In this paper the segregation results are evaluated qualitatively and

quantitatively by the segregation pattern and the segregation degree

respectively The particle bed is 1047297

rstly 1047298

uidized for a certain time andthen the 1047298uidizing air is suddenly shut down The static particle bed is

divided into 1047297ve layers evenly in the axial direction and we take sam-

ples from each layer to test the ash content The segregation pattern is

obtained by plotting these ash content data with the dimensionless

bed height H lowast=H i H 0 as Y-axis where H i is the average bed height of

the ith sampling layer and H 0 is the total bed height of the static bed

A statistical indicator S is proposed to evaluate the segregation degree

quantitatively and the de1047297nition is shown in Eq (1)

S frac14

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Xn

ifrac141

Ai= A0minus1eth THORN2

nminus1

v uuut

eth1THORN

where Ai isthe ash content of coal ofthe ith sampling point A0 is the ini-

tial ash content of feed coal and n is the total sampling number It can

be clearly inferred from Eq (1) that when a granular system is perfectly

mixed Ai= A0 S =0 and a largervalueof S indicates better segregation

that is favorable for 1047297ne coal separation

4 Results and discussion

41 Effect of super 1047297cial air velocity on segregation

In a vibrated gas-1047298uidized bed the steady state of the granular sys-

tem is a result of the dynamic equilibrium between the competing pro-

cesses of mixing and segregation [14] The super1047297cial air velocity playsa critical role in achieving the optimal segregation results Besides the

dispersion uniformity of the 1047298uidizing air also has a signi1047297cant in1047298uence

on the bubble characteristics The optimal air velocity for segregation

highly depends on several factors including particle properties vibration

energy and bed height Thus a dimensionless super1047297cial air velocity

U lowast=(U minusU mb) U mb is introduced to study theeffect of super1047297cial air ve-

locity on segregation where U and U mb is the 1047298uidizing air velocity and

the minimum bubbling air velocity respectively

Fig 2 depicts the segregation results of the two types of feed coal

at different super1047297cial air velocities It can be seen that the two curves

both exhibit inverted V-shape and have single peak value that corre-

sponds to the best segregation degree For minus6+3 mm size feed coal

the U lowast value at this peak is equal to 02 while it is 015 forminus3+1 mm

Table 1

Results of the sink-1047298oat experiment of minus6+ 3 mm size fraction of coal

Density fraction

(gcm3)

Average density (gcm3) Weight fraction () Ash content ()

minus13 125 412 602

+13ndash14 135 2464 1031

+14ndash15 145 1694 1834

+15ndash16 155 606 2583

+16ndash17 165 292 3500

+17ndash18 175 685 4452

+18 22 3847 7597

Total 10000 4076

Table 2

Results of the sink-1047298oat experiment of minus3+ 1 mm size fraction of coal

Density fraction

(gcm3)

Average density (gcm3) Weight fraction () Ash content ()

minus13 125 602 581

+13ndash14 135 2352 1138

+14ndash15 145 1675 1768

+15ndash16 155 965 2424

+16ndash17 165 296 3681

+17ndash18 175 342 4424+18 22 3768 7652

Total 10000 3976

8

7

6

54

32

19

10 11

12

Fig 1 Schematic diagram of the experimental apparatus 1 Air 1047297lter 2 Roots blower

3 Tank 4 Pressure gauge 5 Valve 6 Rotameter 7 Vibrated bed 8 Air chamber 9

Air distributor 10 Vessel 11 High-speed camera 12 Image analysis system

339 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343

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size feed coal When the super1047297cial air velocity is larger than U mb the

excess air produces bubbles that divide the bed into particulate phase

and bubble phase Cibilaro and Rowe [12] pointed out that the mixing

and segregation processes in a gasndashsolid 1047298uidized bed mainly depend

on the bubbles Thus the bubble characteristics including bubble size

and bubble rise velocity signi1047297cantly determine the segregation

performance

Appropriate super1047297cial air velocity can generate the bubbles that

lead to the optimal segregation results When the bubble size is too

small there is no enough space for particle settling in the disturbed

region below the rising bubble When the bubble size is too big the

bubble rise velocity becomes too fast to provide enough time for par-

ticle settling in the disturbed region

42 Effect of vibration intensity on segregation

The verticalvibration may convenientlybe characterized by vibration

intensityΓ = Aω 2 g where A is the amplitude of the oscillationω =2π f is

the angular frequency f is the frequency of the oscillation and Γ is theratio of the maximum acceleration of the bed to the acceleration due to

gravity g The value range of A and the frequency f are 05ndash3 mm and

10ndash50 Hz respectively The minus6+3 mm and minus3+1 mm size friction

coal is separated at U lowast=015020 respectively under different vibration

intensity The segregation degree of the two types of feed coal is shown

in Fig 3 It can be seen that the two curves both exist with single peak

value which leads to the optimal segregation results In a vibrated

gas-1047298uidized bed of coarse particles the input vibration energy can

generate appropriate 1047298uidizing conditions for particle segregation by

eliminating the channeling of air 1047298ow within the bed and optimizing

the bubble characteristics due primarily to enhanced particle interaction

and particle piercing behavior However when the input vibration ener-

gy excesses the critical value the particle motion in the lower section of

the bed becomes severe enough to deteriorate thehindered settling pro-

cess which will lead to comparatively good mixing of the particle bed

43 Effect of bed height on segregation

Fig 4 depicts the segregation results of the two types of feed coal

with different initial bed height (H ) It can be seen that when bed

height is smaller than 70 mm the patterns of the two curves are

1047298at which indicates that the segregation degrees of the two types

of feed coal are both uniform But when the bed height is larger

than 70 mm the segregation performance of the two types of feed

coal both deteriorates dramatically This change is mainly derived

from the weaknesses of the vibration function to the 1047298uidizing condi-tion of the upper section of the particle bed when the bed height ex-

ceeds this critical value In addition bubble size at the upper section

of the bed with large bed height will become large enough to cause

large-scale particle circulations that deteriorate the segregation

process

44 Effect of 1047298uidizing time on segregation

According to the aforementioned separation mechanism the opti-

mal segregation requires enough bubble-driven jigging cycles in order

to provide enough time for particle segregation primarily depending

on the density differences Fig 5 demonstrates the segregation degree

of the two types of feed coal at different 1047298uidizing time We can see

clearly that the segregation degree of the two types of feed coal both in-creases with the 1047298uidizing time until it reaches to a critical value at

2 min and then the curves become 1047298at when the 1047298uidizing time ex-

ceeds 2 min These curves indicate that the two granular systems both

achieve a stable state of segregation after 2 min 1047298uidization and then

there is no improvement when enlarging the 1047298uidizing time

45 Veri 1047297cation of bubble-driven jigging mechanism

The aforementioned bubble-driven jigging mechanism canbe veri1047297ed

by theresults of image analysis of thepictures that are photographed by a

high-speed camera shown in Fig 6 Three particles labeled by 1 2 and 3

with particle size of minus3+1 mm represent clean coal gangue and mid-

dlings respectively These three particles are identi1047297ed visually by the dif-

ference in physical properties like shape color and luster using the image

50 60 70 80 90 100 110051

054

057

060

063

066

069

S

H (mm)

-3+1 mm

-6+3 mm

Fig 4 Segregation degree at different bed height

Fig 3 Segregation degree at different vibration intensity

005 010 015 020 025

02

03

04

05

06

07

-6+3 mm

-3+1 mm

S

U

Fig 2 Segregation degree at different super1047297cial gas velocities

340 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343

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magni1047297cation method and the identi1047297cation is concretely given in

Table 3 At 0 ms particles in the local region investigated are compact

and there are no visible particle motions When a bubble passes through

this region since 165 ms particles in this region become loose and differ-

ent in motion Particle 1 with lower density moves upwards along with

the bubble due to gas drag force while particle 2 and particle 3 settle

through the bubble quickly Since 615 ms in the disturbed region

below the bubble particle 2 settles faster than particle 3 And 1047297nally

after a bubble-driven jigging cycle the three investigated particles at

1065 ms are arranged in the axial direction with particle 1 (clean coal)

in the top particle 3 (middlings) in the middle and particle 2 (gangue)

in the bottom which is extremely consistent with the above description

of the bubble-driven jigging mechanism

46 Separation performance

Fig 7 depicts the segregation patterns corresponding to the opti-

mal segregation performance of the two types of feed coal and the

corresponding values of the aforementioned factors are listed inTable 4 Under this optimal conditions each feed coal is 1047297rstly sepa-

rated at a higher separation density to discharge thegangue andthen

the gangue-free coal is separated at a lower separation density to

produce the clean coal and the middlings The partition distribution of

three products of each feed coal is examined by carrying out the

sink-1047298oat experiments as given in Tables 5 and 6 respectively Based on

these data the partition curves of the two types of feed coal are plotted

in Fig 8 The separation results of the two types of feed coal are given in

Table 7 The probable error E values of minus6+3 mm and minus3+1 mm

size fraction of feed coal are 019ndash0225 and 0175ndash0195 respectively

With the comparison of the E value theminus3+ 1 mmfeed coalhasa better

separation ef 1047297ciency both at a high separation densityand a low one than

the minus6+3 mm feed coal This is because that minus3+1 mm feed coal is

easier to achieve uniform 1047298uidization with good bubbling behavior than

minus6+ 3 mm feed coal For each feed coal the E value at a high separation

density is smaller than that at a low one

5 Conclusion

In this study we focus on utilizing the segregation in a vibrated

gas-1047298uidized bed to provide a solution to the dif 1047297cult problem of 1047297ne

coal separation in a dry process which is greatly meaningful with re-

spect to the utilization of 1047297ne coal for energy resources in North-West

China In this process bubble-driven jigging cycles provide enough

space and time for the particles to segregate in the axial direction

depending on their hindered settling velocity differences The experi-

mental results show that the operational parameters including super1047297-

cial air velocity vibration intensity bed height and1047298uidizing time have

signi1047297cant in1047298uences on the segregation performance and the probablyerror E values of minus6+ 3 mm and minus3+1 mm size fraction of feed coal

are 019ndash0225 and 0175ndash0195 respectively According to the analysis

Fig 6 Particle segregation in a bubble-driven jigging cycle

Table 3

Physical properties of the clean coal middlings and gangue particles

Item Color Luster Shape

Clean coal Black Submetallicvitreous luster Round short-rod ellipse

Middlings Dark gray Bituminous luster Long-rod cuboid

Gangue Gray Dull luster Sheet strip

0 1 2 3 4035

040

045

050

055

060

065

070

075

S

T (min)

-6+3 mm

-3+1 mm

Fig 5 Segregation degree at different 1047298uidizing time

341 X Yang e t al Fuel Processing Technology 106 (2013) 338ndash 343

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size feed coal When the super1047297cial air velocity is larger than U mb the

excess air produces bubbles that divide the bed into particulate phase

and bubble phase Cibilaro and Rowe [12] pointed out that the mixing

and segregation processes in a gasndashsolid 1047298uidized bed mainly depend

on the bubbles Thus the bubble characteristics including bubble size

and bubble rise velocity signi1047297cantly determine the segregation

performance

Appropriate super1047297cial air velocity can generate the bubbles that

lead to the optimal segregation results When the bubble size is too

small there is no enough space for particle settling in the disturbed

region below the rising bubble When the bubble size is too big the

bubble rise velocity becomes too fast to provide enough time for par-

ticle settling in the disturbed region

42 Effect of vibration intensity on segregation

The verticalvibration may convenientlybe characterized by vibration

intensityΓ = Aω 2 g where A is the amplitude of the oscillationω =2π f is

the angular frequency f is the frequency of the oscillation and Γ is theratio of the maximum acceleration of the bed to the acceleration due to

gravity g The value range of A and the frequency f are 05ndash3 mm and

10ndash50 Hz respectively The minus6+3 mm and minus3+1 mm size friction

coal is separated at U lowast=015020 respectively under different vibration

intensity The segregation degree of the two types of feed coal is shown

in Fig 3 It can be seen that the two curves both exist with single peak

value which leads to the optimal segregation results In a vibrated

gas-1047298uidized bed of coarse particles the input vibration energy can

generate appropriate 1047298uidizing conditions for particle segregation by

eliminating the channeling of air 1047298ow within the bed and optimizing

the bubble characteristics due primarily to enhanced particle interaction

and particle piercing behavior However when the input vibration ener-

gy excesses the critical value the particle motion in the lower section of

the bed becomes severe enough to deteriorate thehindered settling pro-

cess which will lead to comparatively good mixing of the particle bed

43 Effect of bed height on segregation

Fig 4 depicts the segregation results of the two types of feed coal

with different initial bed height (H ) It can be seen that when bed

height is smaller than 70 mm the patterns of the two curves are

1047298at which indicates that the segregation degrees of the two types

of feed coal are both uniform But when the bed height is larger

than 70 mm the segregation performance of the two types of feed

coal both deteriorates dramatically This change is mainly derived

from the weaknesses of the vibration function to the 1047298uidizing condi-tion of the upper section of the particle bed when the bed height ex-

ceeds this critical value In addition bubble size at the upper section

of the bed with large bed height will become large enough to cause

large-scale particle circulations that deteriorate the segregation

process

44 Effect of 1047298uidizing time on segregation

According to the aforementioned separation mechanism the opti-

mal segregation requires enough bubble-driven jigging cycles in order

to provide enough time for particle segregation primarily depending

on the density differences Fig 5 demonstrates the segregation degree

of the two types of feed coal at different 1047298uidizing time We can see

clearly that the segregation degree of the two types of feed coal both in-creases with the 1047298uidizing time until it reaches to a critical value at

2 min and then the curves become 1047298at when the 1047298uidizing time ex-

ceeds 2 min These curves indicate that the two granular systems both

achieve a stable state of segregation after 2 min 1047298uidization and then

there is no improvement when enlarging the 1047298uidizing time

45 Veri 1047297cation of bubble-driven jigging mechanism

The aforementioned bubble-driven jigging mechanism canbe veri1047297ed

by theresults of image analysis of thepictures that are photographed by a

high-speed camera shown in Fig 6 Three particles labeled by 1 2 and 3

with particle size of minus3+1 mm represent clean coal gangue and mid-

dlings respectively These three particles are identi1047297ed visually by the dif-

ference in physical properties like shape color and luster using the image

50 60 70 80 90 100 110051

054

057

060

063

066

069

S

H (mm)

-3+1 mm

-6+3 mm

Fig 4 Segregation degree at different bed height

Fig 3 Segregation degree at different vibration intensity

005 010 015 020 025

02

03

04

05

06

07

-6+3 mm

-3+1 mm

S

U

Fig 2 Segregation degree at different super1047297cial gas velocities

340 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343

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magni1047297cation method and the identi1047297cation is concretely given in

Table 3 At 0 ms particles in the local region investigated are compact

and there are no visible particle motions When a bubble passes through

this region since 165 ms particles in this region become loose and differ-

ent in motion Particle 1 with lower density moves upwards along with

the bubble due to gas drag force while particle 2 and particle 3 settle

through the bubble quickly Since 615 ms in the disturbed region

below the bubble particle 2 settles faster than particle 3 And 1047297nally

after a bubble-driven jigging cycle the three investigated particles at

1065 ms are arranged in the axial direction with particle 1 (clean coal)

in the top particle 3 (middlings) in the middle and particle 2 (gangue)

in the bottom which is extremely consistent with the above description

of the bubble-driven jigging mechanism

46 Separation performance

Fig 7 depicts the segregation patterns corresponding to the opti-

mal segregation performance of the two types of feed coal and the

corresponding values of the aforementioned factors are listed inTable 4 Under this optimal conditions each feed coal is 1047297rstly sepa-

rated at a higher separation density to discharge thegangue andthen

the gangue-free coal is separated at a lower separation density to

produce the clean coal and the middlings The partition distribution of

three products of each feed coal is examined by carrying out the

sink-1047298oat experiments as given in Tables 5 and 6 respectively Based on

these data the partition curves of the two types of feed coal are plotted

in Fig 8 The separation results of the two types of feed coal are given in

Table 7 The probable error E values of minus6+3 mm and minus3+1 mm

size fraction of feed coal are 019ndash0225 and 0175ndash0195 respectively

With the comparison of the E value theminus3+ 1 mmfeed coalhasa better

separation ef 1047297ciency both at a high separation densityand a low one than

the minus6+3 mm feed coal This is because that minus3+1 mm feed coal is

easier to achieve uniform 1047298uidization with good bubbling behavior than

minus6+ 3 mm feed coal For each feed coal the E value at a high separation

density is smaller than that at a low one

5 Conclusion

In this study we focus on utilizing the segregation in a vibrated

gas-1047298uidized bed to provide a solution to the dif 1047297cult problem of 1047297ne

coal separation in a dry process which is greatly meaningful with re-

spect to the utilization of 1047297ne coal for energy resources in North-West

China In this process bubble-driven jigging cycles provide enough

space and time for the particles to segregate in the axial direction

depending on their hindered settling velocity differences The experi-

mental results show that the operational parameters including super1047297-

cial air velocity vibration intensity bed height and1047298uidizing time have

signi1047297cant in1047298uences on the segregation performance and the probablyerror E values of minus6+ 3 mm and minus3+1 mm size fraction of feed coal

are 019ndash0225 and 0175ndash0195 respectively According to the analysis

Fig 6 Particle segregation in a bubble-driven jigging cycle

Table 3

Physical properties of the clean coal middlings and gangue particles

Item Color Luster Shape

Clean coal Black Submetallicvitreous luster Round short-rod ellipse

Middlings Dark gray Bituminous luster Long-rod cuboid

Gangue Gray Dull luster Sheet strip

0 1 2 3 4035

040

045

050

055

060

065

070

075

S

T (min)

-6+3 mm

-3+1 mm

Fig 5 Segregation degree at different 1047298uidizing time

341 X Yang e t al Fuel Processing Technology 106 (2013) 338ndash 343

7172019 Artikel 3

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magni1047297cation method and the identi1047297cation is concretely given in

Table 3 At 0 ms particles in the local region investigated are compact

and there are no visible particle motions When a bubble passes through

this region since 165 ms particles in this region become loose and differ-

ent in motion Particle 1 with lower density moves upwards along with

the bubble due to gas drag force while particle 2 and particle 3 settle

through the bubble quickly Since 615 ms in the disturbed region

below the bubble particle 2 settles faster than particle 3 And 1047297nally

after a bubble-driven jigging cycle the three investigated particles at

1065 ms are arranged in the axial direction with particle 1 (clean coal)

in the top particle 3 (middlings) in the middle and particle 2 (gangue)

in the bottom which is extremely consistent with the above description

of the bubble-driven jigging mechanism

46 Separation performance

Fig 7 depicts the segregation patterns corresponding to the opti-

mal segregation performance of the two types of feed coal and the

corresponding values of the aforementioned factors are listed inTable 4 Under this optimal conditions each feed coal is 1047297rstly sepa-

rated at a higher separation density to discharge thegangue andthen

the gangue-free coal is separated at a lower separation density to

produce the clean coal and the middlings The partition distribution of

three products of each feed coal is examined by carrying out the

sink-1047298oat experiments as given in Tables 5 and 6 respectively Based on

these data the partition curves of the two types of feed coal are plotted

in Fig 8 The separation results of the two types of feed coal are given in

Table 7 The probable error E values of minus6+3 mm and minus3+1 mm

size fraction of feed coal are 019ndash0225 and 0175ndash0195 respectively

With the comparison of the E value theminus3+ 1 mmfeed coalhasa better

separation ef 1047297ciency both at a high separation densityand a low one than

the minus6+3 mm feed coal This is because that minus3+1 mm feed coal is

easier to achieve uniform 1047298uidization with good bubbling behavior than

minus6+ 3 mm feed coal For each feed coal the E value at a high separation

density is smaller than that at a low one

5 Conclusion

In this study we focus on utilizing the segregation in a vibrated

gas-1047298uidized bed to provide a solution to the dif 1047297cult problem of 1047297ne

coal separation in a dry process which is greatly meaningful with re-

spect to the utilization of 1047297ne coal for energy resources in North-West

China In this process bubble-driven jigging cycles provide enough

space and time for the particles to segregate in the axial direction

depending on their hindered settling velocity differences The experi-

mental results show that the operational parameters including super1047297-

cial air velocity vibration intensity bed height and1047298uidizing time have

signi1047297cant in1047298uences on the segregation performance and the probablyerror E values of minus6+ 3 mm and minus3+1 mm size fraction of feed coal

are 019ndash0225 and 0175ndash0195 respectively According to the analysis

Fig 6 Particle segregation in a bubble-driven jigging cycle

Table 3

Physical properties of the clean coal middlings and gangue particles

Item Color Luster Shape

Clean coal Black Submetallicvitreous luster Round short-rod ellipse

Middlings Dark gray Bituminous luster Long-rod cuboid

Gangue Gray Dull luster Sheet strip

0 1 2 3 4035

040

045

050

055

060

065

070

075

S

T (min)

-6+3 mm

-3+1 mm

Fig 5 Segregation degree at different 1047298uidizing time

341 X Yang e t al Fuel Processing Technology 106 (2013) 338ndash 343

7172019 Artikel 3

httpslidepdfcomreaderfullartikel-3-568d98f1db858 56

of three product separation results the1047297ne coalseparation in a vibrated

gas-1047298uidized bed system is useful to and more effective for 1047297ne coal

cleaning in drought and cold regions

Acknowledgments

The research work involved in this paper received the 1047297nancial

support by the National Natural Science Foundation (No 51134022

51174203) the Key Project of Chinese National Programs for Fundamen-

tal Research and Development (973 program) (No 2012CB214904) the

National Natural Science Foundation of China for Innovative Research

Group (No 50921002) the Natural Science Foundation of Jiangsu Prov-

ince of China (No BK2010002) the Fundamental Research Funds for

the Central Universities (No 2010QNB11 2010ZDP01A06)

a

b

Fig 7 The optimal segregation patterns of the two types of feed coal

Table 4

Operational conditions leading to the optimal segregation performance of the two

types of the feed coal

Factors minus6+3 mm minus3+1 mm

U lowast 02 015

Γ 023 02

H (mm) 70 70

T (minutes) 2 2

Table 6

The sink-1047298oat results of the products of minus6+3 mm feed coal

Density

fraction

( g cm3)

Product weight fraction () Calculated feedstock () Partition

coef 1047297cient ()

Gangue Middlings Clean

coal

Total Reconcentration High

density

Low

density

minus13 015 054 321 390 375 391 1430

13ndash14 142 497 1825 2464 2322 576 2141

14ndash15 110 537 877 1524 1414 721 3797

15ndash16 072 317 326 716 644 1017 4929

16ndash17 057 174 121 352 295 1628 5915

17ndash18 250 390 144 784 534 3185 7304

+18 3338 385 048 3770 433 8852 8893

Total 3984 2354 3662 10000 6016

Table 5

The sink-1047298oat results of the products of minus3+1 mm feed coal

Density

fraction

( g cm3)

Product weight fraction () Calculated feedstock () Partition

coef 1047297cient ()

Gangue Middlings Clean

coal

Total Reconcentration High

density

Low

density

minus13 020 088 455 563 544 346 1626

13ndash14 087 455 1847 2389 2302 363 1978

14ndash15 098 568 977 1643 1545 597 3675

15ndash16 086 458 315 858 772 997 5927

16ndash17 042 153 069 263 222 1583 6895

17ndash18 212 121 041 374 162 5672 7492

+18 3477 386 046 3910 433 8893 8926

Total 40 21 2229 3750 10000 5979

12 14 16 18 20 22

0

20

40

60

80

100

P a r t i t i o n c o e f f i c i e n t ( )

Density (gcm3)

High-density separation

Low-density separation

-3+1 mm

12 14 16 18 20 22

0

20

40

60

80

100

-6+3 mm

High-density separation

Low-density separation

P a r t i t i o n c o e f f i c i e n t (

)

Density (gcm3)

a

b

Fig 8 Partition curves of the two types of feed coal

342 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343

7172019 Artikel 3

httpslidepdfcomreaderfullartikel-3-568d98f1db858 66

References

[1] Y Zhao L Tang Z Luo C Liang H Xing W Wu C Duan Experimental and numericalsimulation studies of the 1047298uidization characteristics of a separating gasndashsolid 1047298uidizedbed Fuel Processing Technology 91 (2) (2010) 1819ndash1825

[2] AK Sahu A Tripathy SK Biswal A Parida Stability study of an air dense medium1047298uidized bed separator for bene1047297ciation of high-ashIndian coal International Journalof Coal Preparation and Utilization 31 (3ndash4) (2011) 127ndash148

[3] CH Sampaio W Aliaga ET Pacheco E Petter H Wotruba Coal bene1047297ciation of Candiota mine by dry jigging Fuel Processing Technology 89 (2) (2008) 198ndash202

[4] B Zhang H Akbari F Yang MKMohanty J Hirschi Performance optimizationof the FGX dry separator for cleaning high-sulfur coal International Journal of CoalPreparation and Utilization 31 (3ndash4) (2011) 161ndash186

[5] M Fan Q Chen Y Zhao Z Luo Fine coal (6ndash1 mm) separation in magneticallystabilized 1047298uidized beds International Journal of Mineral Processing 63 (4)(2001) 225ndash232

[6] M Fan Q Chen Y Zhao Z Luo Y Guan Fundamentals of a magnetically stabilized1047298uidized bed for coal separation International Journal of Coal Preparation andUtilization 23 (1) (2003) 47ndash55

[7] Z Luo M Fan Y Zhao X Tao Q Chen Z Chen Density-dependent separation of dry 1047297ne coal in a vibrated 1047298uidized bed Powder Technology 187 (2) (2008)

119ndash

123[8] SA Macpherson SM Iveson KP Galvin Density based separations in the Re1047298uxClassi1047297er with an airumlCsand denseumlCmedium and vibration Minerals Engineering23 (2) (2010) 74ndash82

[9] SA Macpherson SM Iveson KP Galvin Density-based separation in a vibratedRe1047298ux Classi1047297erwithan airndashsand densendashmedium tracerstudies with simultaneousunder1047298owand over1047298ow removal Minerals Engineering 24 (10) (2011) 1046ndash1052

[10] PN Rowe AW Nienow Particle mixing and segregation in gas 1047298uidised beds Areview Powder Technology 15 (2) (1976) 141ndash147

[11] D Geldart Types of gas 1047298uidization Powder Technology 7 (5) (1973) 285ndash292[12] LG Gibilaro PN Rowe A model for a segregating gas 1047298uidised bed Chemical

Engineering Science 29 (6) (1974) 1403ndash1412[13] JF Davidson R Clift D Harrison Fluidization 2nd edn Academic Press Landon

1985[14] NS Naimer T Chiba AW Nienow Parameter estimation for a solids mixing

segregation model for gas 1047298uidised beds Chemical Engineering Science 37 (7)(1982) 1047ndash1057

Table 7

Separation results of 1047297ne coal in a vibrated gas-1047298uidized bed

Separation results minus6+3 mm minus3+1 mm

Feed ash content () 4076 3976

Low separation density ( g cm3) 155 152

High separation density ( g cm3) 189 177

Low density separation E 0225 0195

High density separation E 019 0175

Clean coal ash content () 1556 1442

Clean coal yield () 3662 3750Middlings ash content () 3247 3016

Middlings yield () 2354 2229

Gangue ash content () 7007 7102

Gangue yield () 3984 4021

343 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343

7172019 Artikel 3

httpslidepdfcomreaderfullartikel-3-568d98f1db858 66

References

[1] Y Zhao L Tang Z Luo C Liang H Xing W Wu C Duan Experimental and numericalsimulation studies of the 1047298uidization characteristics of a separating gasndashsolid 1047298uidizedbed Fuel Processing Technology 91 (2) (2010) 1819ndash1825

[2] AK Sahu A Tripathy SK Biswal A Parida Stability study of an air dense medium1047298uidized bed separator for bene1047297ciation of high-ashIndian coal International Journalof Coal Preparation and Utilization 31 (3ndash4) (2011) 127ndash148

[3] CH Sampaio W Aliaga ET Pacheco E Petter H Wotruba Coal bene1047297ciation of Candiota mine by dry jigging Fuel Processing Technology 89 (2) (2008) 198ndash202

[4] B Zhang H Akbari F Yang MKMohanty J Hirschi Performance optimizationof the FGX dry separator for cleaning high-sulfur coal International Journal of CoalPreparation and Utilization 31 (3ndash4) (2011) 161ndash186

[5] M Fan Q Chen Y Zhao Z Luo Fine coal (6ndash1 mm) separation in magneticallystabilized 1047298uidized beds International Journal of Mineral Processing 63 (4)(2001) 225ndash232

[6] M Fan Q Chen Y Zhao Z Luo Y Guan Fundamentals of a magnetically stabilized1047298uidized bed for coal separation International Journal of Coal Preparation andUtilization 23 (1) (2003) 47ndash55

[7] Z Luo M Fan Y Zhao X Tao Q Chen Z Chen Density-dependent separation of dry 1047297ne coal in a vibrated 1047298uidized bed Powder Technology 187 (2) (2008)

119ndash

123[8] SA Macpherson SM Iveson KP Galvin Density based separations in the Re1047298uxClassi1047297er with an airumlCsand denseumlCmedium and vibration Minerals Engineering23 (2) (2010) 74ndash82

[9] SA Macpherson SM Iveson KP Galvin Density-based separation in a vibratedRe1047298ux Classi1047297erwithan airndashsand densendashmedium tracerstudies with simultaneousunder1047298owand over1047298ow removal Minerals Engineering 24 (10) (2011) 1046ndash1052

[10] PN Rowe AW Nienow Particle mixing and segregation in gas 1047298uidised beds Areview Powder Technology 15 (2) (1976) 141ndash147

[11] D Geldart Types of gas 1047298uidization Powder Technology 7 (5) (1973) 285ndash292[12] LG Gibilaro PN Rowe A model for a segregating gas 1047298uidised bed Chemical

Engineering Science 29 (6) (1974) 1403ndash1412[13] JF Davidson R Clift D Harrison Fluidization 2nd edn Academic Press Landon

1985[14] NS Naimer T Chiba AW Nienow Parameter estimation for a solids mixing

segregation model for gas 1047298uidised beds Chemical Engineering Science 37 (7)(1982) 1047ndash1057

Table 7

Separation results of 1047297ne coal in a vibrated gas-1047298uidized bed

Separation results minus6+3 mm minus3+1 mm

Feed ash content () 4076 3976

Low separation density ( g cm3) 155 152

High separation density ( g cm3) 189 177

Low density separation E 0225 0195

High density separation E 019 0175

Clean coal ash content () 1556 1442

Clean coal yield () 3662 3750Middlings ash content () 3247 3016

Middlings yield () 2354 2229

Gangue ash content () 7007 7102

Gangue yield () 3984 4021

343 X Yang et al Fuel Processing Technology 106 (2013) 338ndash 343